value-axis is an axis of
a chart-widget
that indicates the magnitude of the displayed data values. This
property value is an instance of the value-axis class, and holds properties
that determine how the axis is drawn and the range of values that it
displays.

The value of this property is always a value-axis instance. If you do not pass
a value-axis instance as the value of
the :value-axis initarg when creating a
chart-widget, then a default instance is created automatically.

If there are multiple chart objects (see chart-objects), then some of the
objects may use this value axis while others use the secondary value
axis that is in the value-axis-2 property.